AUTHOR=Cai Xinyue , Zhao Honghai , Liang Chen , Li Min , Liu Runjin 

TITLE=Effects and Mechanisms of Symbiotic Microbial Combination Agents to Control Tomato Fusarium Crown and Root Rot Disease

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.629793

DOI=10.3389/fmicb.2021.629793

ISSN=1664-302X

ABSTRACT=<p>This study evaluated the effects and underlying mechanisms of different combinations of plant symbiotic microbes, comprising arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), and <italic>Trichoderma</italic> spp., on tomato <italic>Fusarium</italic> crown and root rot (TFCRR) resistance. A total of 54 treatments were applied in a greenhouse pot experiment to tomato (<italic>Solanum lycopersicum</italic>) seedlings inoculated with or without <italic>Funneliformis mosseae</italic> (Fm), <italic>Rhizophagus intraradices</italic> (Ri), <italic>Trichoderma virens</italic> l40012 (Tv), <italic>Trichoderma harzianum</italic> l40015 (Th), <italic>Bacillus subtilis</italic> PS1-3 (Bs), <italic>Pseudomonas fluorescens</italic> PS2-6 (Pf), and <italic>Fusarium oxysporum</italic> f. sp. <italic>radicis-lycopersici</italic> (Fo). The symbioses on the tomato root system were well developed, and the composite symbiont generated by AMF + <italic>Trichoderma</italic> spp. was observed for the first time. Compared with other treatments, Ri + Bs + Tv and Fm + Pf + Tv stimulated the greatest improvements in tomato growth and yield. The combination Ri + Pf + Th + Fo resulted in the strongest biocontrol effects on TFCRR, followed by the treatments Th + Pf + Fo and Ri + Th + Fo. Compared with the Fo treatment, most inoculation treatments improved photosynthetic performance and significantly increased defense enzyme activity in tomato plants, of which the treatment Ri + Pf + Th + Fo showed the highest enzyme activity. Metabolome analysis detected changes in a total of 1,266 metabolites. The number of up-regulated metabolites in tomato plants inoculated with Ri + Pf + Th and Ri + Pf + Th + Fo exceeded that of the Fo treatment, whereas the number of down-regulated metabolites showed the opposite trend. It is concluded that AMF + <italic>Trichoderma</italic> + PGPR is the most effective combination to promote resistance to TFCRR in tomato. The up-regulation and down-regulation of metabolites regulated by symbiotic microbial genes may be an important mechanism by which root symbiotic microorganisms promote plant growth, increase yield, and improve disease resistance.</p>